IV.Error ConsiderationsThere are a

IV.Error ConsiderationsThere are a few error sources mainly in analogue signal handling circuits: phase shifts in input coupling circuits, in the amplifiers, and time delays in the comparators. The phase errors may occur also in the logic circuits and in the AND gates as a result of their time delays. In digital processing the main source of errors may be a low clock frequency for time intervals measurements which may cause large quantization errors. In addition to these error sources, another possible error source is a distortion of the input signals.The errors in the input coupling circuits and in the amplifiers can be eliminated by a selection of proper values of components (long time constants of the coupling RC circuits) and fast operational amplifiers with high input impedances and low input voltage offsets and drifts. Even if these parameters are not suitable, matching of properties of both input analogue channels may lead to the resulting low error phase shift.The time delays in the comparators are of two origins: time delays of the output responses caused by the properties of the comparators (response time, output slew rate) and time delays caused by uncertainties of input comparation voltage levels (error bands of the voltage levels of the comparators true responses, input voltage offsets). The first kind of the time delays can be overcome by a proper selection of the comparator circuits. The second kind of the time delays may be partially eliminated by the input offset compensation. But there is another source of similar phase errors – if the comparation voltage level is not zero and the two input signals havedifferent levels. In this case even the same comparation levels in both comparators fail to avoid the significant time and phase error, as shown in Figure 3.